Dynamic Bandwidth Adjustment in Packet Transport Network

ABSTRACT

A method for adjusting bandwidth in a communications network having a plurality of nodes connected over multiple links with a plurality of services running on the links includes detecting an impairment of a link wherein the impairment invokes a reduction in bandwidth available to the services running on the link, communicating information about the impairment to other nodes in the network and redistributing services between the links to limit a bandwidth required by services running on the impaired link to a value not exceeding the bandwidth available on the impaired link.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/560,187 filed on Nov. 15, 2011, the subject matter of which isincorporated in its entirety herein by reference.

TECHNICAL FIELD

The present invention relates generally to telecommunications networksand, more particularly to, methods, devices and networks for loadsharing in networks with variable link bandwidth.

BACKGROUND

As link bandwidth affect the transmission capacity, variabletransmission capacity presents a problem in networks in terms ofensuring the throughput for which the network is designed. From a mobilebackhaul application point of view, this becomes particularly importantat places in the network with a high amount of aggregated traffic orwhen ring or mesh topologies are deployed due to geographical andresiliency considerations (i.e. unreliable transmission media, etc.). Anetwork 100 with variable link capacity is illustrated in FIG. 1.Network 100 includes nodes 110, 120, 130, 140, 150 and 160 (havingcorresponding switches 112, 122, 132, 142, 152 and 162) and variable orfixed bandwidth links 170 between the various nodes. Service paths 180may be established over at least some of the links 170.

At present, the main packet transport networks are Ethernet and MPLS(Multi Protocol Label Switching). However, new technologies such asMPLS-TP (Transport Profile) are likely to be deployed intelecommunications transport networks. These technologies are generallyclients of the physical transport layers which could be copper, ether oroptical fiber. In networks that utilize microwave links for transport ofEthernet or MPLS packets, degradation due to environmental conditions orother impairments could result in loss of traffic on the microwavelinks.

New packet transport technologies are also being deployed over thephysical layers such as fiber, copper or Ether. In microwave transportnetworks, degradation on microwave links can result in catastrophic lossof services. Existing solutions use protection switching whereredundancies of these microwave links are deployed. However, this is anexpensive solution.

Several technologies operating on variable link bandwidth networks donot take full advantage of the offered bandwidth. The links are oftendimensioned for a guaranteed bandwidth which is a threshold for theavailability of the entire link. If the threshold is exceeded, the linkis made inoperable and will not be used for user traffic. Such staticservice allocation is illustrated in FIG. 2.

A link threshold 240 for guaranteed service may be pre-determined(corresponding approximately to 62.5% in this exemplary scenario). Instate 210, the full bandwidth is available (i.e. greater than the 62.5%threshold) for the services allocated on the link. Therefore, noproblems are encountered. In state 220, the link bandwidth has decreasedto approximately 65% (still greater than the threshold) and somebandwidth is not available (35%). In this state, less bandwidth is madeavailable to the best effort services (i.e. not guaranteed service) andbest effort end-users can potentially experience a slower connection(i.e. service degradation). Guaranteed service end-users can still beprovided service.

In state 230, the link bandwidth has decreased to a level where it isnot possible to sustain the guaranteed services (i.e. less than 62.5%).As the services compete for the same resources, they could potentiallyall experience service degradation or even a service break down. Sinceit is not possible to operate in this state, the link can be shut down.A command signal needs to be sent to all services to take an alternateroute. Transmitting such a signal may not always be possible asbandwidth may not be available to cater for extra bandwidth needed bythe service.

A need exists, therefore, for facilitating a desirable throughputsolution directed to networks having links with variable capacity.

SUMMARY

It should be emphasized that the terms “comprises” and “comprising”,when used in this specification, are taken to specify the presence ofstated features, integers, steps or components; but the use of theseterms does not preclude the presence or addition of one or more otherfeatures, integers, steps, components or groups thereof.

In accordance with an exemplary embodiment, a method for adjustingbandwidth in a communications network with a plurality of nodesconnected over multiple links and having a plurality of services runningon the links is disclosed. The method comprises: detecting an impairmentof a link, the impairment causing a reduction in bandwidth available tothe services running on the link; communicating information about theimpairment to other nodes in the network; and redistributing servicesbetween the links to limit a bandwidth required by services running onthe impaired link to a value not exceeding the bandwidth available onthe impaired link.

In accordance with another exemplary embodiment, a node in acommunication network is disclosed. The network includes a plurality ofnodes connected over multiple links and a plurality of services runningon the links. The node comprises: an impairment detection module fordetecting an impairment in a link used by the node, the impairmentinvoking a reduction in bandwidth available to the services running onthe link; a communication interface for communicating information aboutthe impairment to other nodes in the network; and an impairmentresolution module for redistributing services between the impaired linkand at least one other link.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will be understood byreading the following detailed description in conjunction with thedrawings in which:

FIG. 1 illustrates a network with variable link capacity;

FIG. 2 illustrates a static service allocation with pre-definedthreshold values;

FIG. 3 illustrates a network having a service redistribution function inaccordance with exemplary embodiments;

FIG. 4 illustrates a method in accordance with exemplary embodiments;

FIG. 5 illustrates a network node in accordance with exemplaryembodiments;

FIGS. 6(A)-6(C) illustrate a service redistribution method in accordancewith exemplary embodiments;

FIG. 7 illustrates a service redistribution for a ring network inaccordance with exemplary embodiments; and

FIG. 8 illustrates a service redistribution for a necklace/multi-homednetwork in accordance with exemplary embodiments.

DETAILED DESCRIPTION

The various features of the invention will now be described withreference to the figures, in which like parts are identified with thesame reference characters or numerals.

The various aspects of the invention will now be described in greaterdetail in connection with a number of exemplary embodiments. Tofacilitate an understanding of the invention, many aspects of theinvention are described in terms of sequences of actions to be performedby elements of a computer system or other hardware capable of executingprogrammed instructions. It will be recognized that in each of theembodiments, the various actions could be performed by specializedcircuits (e.g., analog and/or discrete logic gates interconnected toperform a specialized function), by one or more processors programmedwith a suitable set of instructions, or by a combination of both. Theterm “circuitry configured to” perform one or more described actions isused herein to refer to any such embodiment (i.e., one or morespecialized circuits and/or one or more programmed processors).

Moreover, the invention can additionally be considered to be embodiedentirely within any form of computer readable carrier, such assolid-state memory, magnetic disk, or optical disk containing anappropriate set of computer instructions that would cause a processor tocarry out the techniques described herein. Thus, the various aspects ofthe invention may be embodied in many different forms, and all suchforms are contemplated to be within the scope of the invention. For eachof the various aspects of the invention, any such form of embodiments asdescribed above may be referred to herein as “logic configured to”perform a described action, or alternatively as “logic that” performs adescribed action.

According to exemplary embodiments, the outcome of the static serviceallocation (as described above) may be improved by establishing controlover the services that should be sustained on a link during bandwidthdecrease. Some of the services on the link can be blocked andredistributed to other paths through the network in some embodiments.The services on the link can even be blocked without redistribution insome embodiments. As a result of the blocking and redistribution,bandwidth may be freed to facilitate better support for the servicesstill allocated on the link (or for those services sharing path with theblocked service). The redistributable service allocation according toexemplary embodiments can facilitate operation below the pre-determinedthreshold such as state 230 of FIG. 2.

In exemplary embodiments where a network is configured to redistributethe traffic to alternate paths, the correlation in the bandwidthvariation between the different links (i.e. “original” and alternate) isevaluated. Redistribution of traffic between links that experience thesame (or similar) physical conditions may not provide same level ofperformance or resiliency as redistribution over links with diversephysical conditions.

Load sharing methods according to exemplary embodiments may utilizeseveral paths between nodes and can facilitate operation at lowerbandwidths. The availability requirements on the guaranteed traffic perlink can be reduced.

Exemplary embodiments may be applicable to those variations that are toolong to be buffered but not long enough to drive the dimensioning of thenetwork. The redistribution of services has to be completed in a timelymanner such that an end-user's quality of experience (QoE) is notaffected or diminished.

In order to offer a timely response to link bandwidth variationsaffecting a service path, a protective switching analogy may be used. Anexemplary network (or a portion thereof) is illustrated in FIG. 3.Network 300 may include a plurality of nodes 310, 320, 330, 340, 350 and360 (with corresponding switches 312, 322, 332, 342, 352 and 362).Network 300 may also include a plurality of links 370 between the nodes.In the illustrated example, two distribution functions 325 and 355 (oneat each of nodes 320 and 350 respectively) are included.

Preconfigured service paths 380 and 390 may be setup between the serviceredistribution functions (via the links). The pre-configuration may takeplace during network dimensioning. The actual path used 380 (referred toas the “active” path for example) may be determined by theredistribution functions 325 and 355 through active monitoring of theconnectivity over the paths 380 and 390. Paths that are not used, suchas path 390, may be denoted as passive paths. Load sharing over multipleactive paths between two service redistribution functions may also befacilitated according to exemplary embodiments.

While the network of FIG. 3 depicts only one service, additionalservices can be deployed in a similar fashion. A link can then betraversed by multiple services. The variable bandwidth links mayinfluence the redistribution functions by blocking/enabling servicesand, in effect, forcing a redistribution of those services. Exemplaryembodiments provide redistribution per service over different paths in atopology consisting not only of primary and backup paths between twonodes, but also an arbitrary number of ingress and egress points.Multiple links may exist between one set of nodes (such as between nodes310 and 320 for example). Multiple paths may exist between a set ofnodes as well.

Exemplary embodiments for achieving increased capacity and availabilityin networks with variable link bandwidth detect impairment in a link,communicate information about the impairment to other links anddistribute the services from links with reduced bandwidth to other linkshaving the bandwidth available for facilitating the service. Bandwidthrequirement on the impaired links is throttled down to a level that canbe accommodated by the reduced bandwidth.

Impairment may be detected if the link level conditions indicate a needfor relocation of service with a potential gain. Potential gain refersto the ability to use at least some of the available bandwidth (that hasbeen reduced in a degraded link) as opposed to not being able to use anyof the available bandwidth.

Information about the impairment may be communicated for resolution.Signaling between nodes may be used to communicate the impairmentinformation. The

information that is communicated can include the reduced bandwidth valuefor example. For example, if a link is set up with 300 Mbps bandwidthand degradation leads to a bandwidth of 200 Mbps in the link, thereduced bandwidth value (i.e. 200 Mbps) can be communicated to the othernodes. The resolution may include redistributing services on theimpaired links to links which have adequate bandwidth for sustaining thetraffic. The changes in the network resulting from the impairment andredistribution can be communicated to the control plane or networkmanagement system.

The detection of impairment includes finding network states that couldbe gained by a potential redistribution of services. For variablebandwidth networks, this includes having the ability to add services fortransmission to links with available bandwidth.

A link can be used by several services which may have different QoSrequirements. Depending on those requirements and the pattern of thelink bandwidth variation, the services can be affected in differentways. For links where the link speed varies in such a fashion thatbuffering alone can not contribute to service degradation, the service(that is affected by the degradation) may be redistributed to otherpaths through the network.

Services that can be redistributed may be enabled with impairmentdetection for those links where bandwidth variation is dimensioned tooccur. The impairment detection may include evaluating whether theservice can be sustained on the link or it has to be moved to anotherlink. Link degradation may be detected by utilizing performanceparameters for monitoring signal quality. The link capacity may besignaled back to the node from which packets are sent over the link.Performance parameters are known and are used to determine packet loss,error rate, etc.

The PHY mode of a link may be used to detect impairment andredistribution of a service. An evaluation of a buffer may also be madeto determine if service redistribution is warranted (i.e. congestion maybe evaluated on a link in deciding whether to redistribute a service).

There exists a potential for several services to be simultaneouslyimpaired. In exemplary embodiments, a priority scheme may be applied todetermine the order of redistribution of the impaired services. Thepriority may be influenced by factors such as the current linkbandwidth, the QoS requirements of the services, the servicerequirements for bandwidth etc.

If the link improves (i.e. the bandwidth increases to previously setlevels for example), an evaluation of services that could beaccommodated on the link may be triggered.

The impairment detection functionality may be located in the networkelement attached to the variable link function where congestiondetection is possible. This location may be at one or both ends of alink depending on whether symmetric or asymmetric traffic patterns areexpected.

The functionality for detecting impairment may be located at a networklocation that is different from a network location where the impairmentmay be resolved (by redistributing the impacted service for example).Therefore, the detected impairment (and its scope) has to becommunicated to the location of the impairment resolution. This may beaccomplished by letting network elements experiencing impairmentactively block or drop service path monitoring messages. Dropping orblocking service path monitoring messages can signal link impairment.Such impairment can be signaled to the service resolution functionality.

Per service path monitoring message is not limited to a particularprotocol and may be implemented for Ethernet using Ethernet OAM such asCCM (Continuity Check Message) or other performance parameters asdefined in ITU-T Recommendation Y.1731. Similarly, for MPLS/MPLS-TP,MPLS/MPLS-TP OAM such as Hello in BDF (bidirectional forwardingdetection) as defined by the IETF can be used. Communication ofimpairment in this manner is interoperable to already deployed networksand network elements.

If a high-priority service is affected by link degradation, a swiftredistribution has to be performed in order to avoid further degradationof the link. Load sharing on a service level may be achieved by theimplementation of service redistribution according to exemplaryembodiments. The service redistribution function can typically bepre-provisioned with at least two paths. The paths may be an active path380 and a passive path 390 as illustrated in FIG. 3. The alternativepaths may be pre-defined during network provisioning for example.Passive paths are not entirely unutilized. They may be used for lowpriority traffic when not being used as active paths.

While other alternatives (such as dynamic re-routed paths for example,etc.) may also be implemented, the time needed for establishing newpaths or having multiple network elements obtain a converged networkview may negatively affect the user experience beyond a tolerable level.

Network planning, control plane and/or network management systems maycontrol how the network responds to variations in link bandwidth.Network elements detecting impairment and the network elementsimplementing the redistribution function are synchronized according toexemplary embodiments. Since exemplary embodiments are implemented perservice, deployments having more than two network entry/exists aresupported without having to synchronize additional network elements.Service re-routing may be achieved without the need for communicationamong the edge nodes.

During provisioning, a set of rules or conditions may be established forlinks. These rules may specify the action(s) to be taken in case of linkdegradation. The rules may, for example, specify that if bandwidth fallsbelow a particular level in a link, then a service has to beredistributed to another link/path. The service that is to beredistributed, and the link to which it is to be redistributed, may alsobe specified. Rules that are specific to each node may be located at thephysical layer for each node; rules for the network may be located atthe control plane and/or the network management system (NMS).

Different types of services may be affected differently when, on onehand, they run on variable bandwidth links and on the other hand, theyare subjected to redistribution to a new path.

Non-time critical services (best effort service) may handle variationsin bandwidth better than real-time services (guaranteed service). Fornon-time critical services, the traffic may be buffered more extensivelyand since the service does not have a strict delivery deadline, a goodQoE may be offered. Extensive buffering on real-time service, however,may degrade the user QoE.

For best effort traffic based predominantly on TCP (Transmission ControlProtocol), if a link has been subjected to bandwidth decrease (i.e.invoked by link degradation), the link becomes the congestion point forone or several TCP flows. The link buffer may be used by the TCP AIMD(Additive Increase/Multiplicative Decrease) congestion avoidancemechanism to handle congestion and maintain a high TCP throughput. Incase that the service is switched over to a different path, the contentsof the buffer can be discarded. The switch and loss of packet(s) candisturb the TCP session and thus reduce the throughput compared toletting the buffer sustains the throughput.

By reacting to congestion scenarios by redistribution, TCP flows mightend up in a slow start phase. Due to the exponential traffic growthduring slow start of several TCP flows, disturbance may also occur onthe backup path.

For TCP based traffic, with TCP being opportunistic, buffer build-up maynot be an accurate indicator of service degradation. On the other hand,if proper capacity

planning has been conducted, then for high-priority non-TCP basedtraffic, buffer build-up may be a good indication of the commencement ofservice degradation.

The allocation and redistribution of services in variable link bandwidthnetworks may redistribute real-time services before redistributing besteffort services. The timing requirements for real-time services,however, are strict.

A method in accordance with exemplary embodiments is illustrated in FIG.4. Method 400 of FIG. 4 may include impairment detection at 410,impairment communication at 420 and impairment resolution at 430.Impairment communication may include communicating the impairment toother nodes. Impairment resolution may include redistribution ofservices.

A node in accordance with exemplary embodiments is illustrated in FIG.5. Node 500 may include an impairment detection module 510, acommunication interface 520 and impairment resolution module 530. Thefunctionality of modules 510 and 530 was described above. Thecommunication interface 520 communicates the impairment detection toother nodes in the network and also facilitates communication betweenmodules 510 and 530. As a result of service redistribution that isperformed module 530 to resolve an impairment, the bandwidth required byservices running on the impaired link is reduced so that it does notexceed the available bandwidth.

In some embodiments, the interface 520 may be separated into twofunctional units, one for communication with the other nodes in thenetwork and one for communication between the impairment detectionmodule 510 and the impairment mitigation module 530.

Interface 520 can communicate, to the other nodes, the bandwidthavailable after the impairment and the services running on the link usedby the node. Interface 520 can also receive, from the other nodes,information about bandwidth available on links used by the other nodesand services running on those links.

Modules 510, 520 and 530 can be implemented in one hardware block 540 orin node 500 as separate hardware modules. Traffic congestion may also bemonitored on a link using a fixed or configurable threshold setting. Thebuffer may be monitored for example and if the information in the bufferexceeds a pre-determined threshold, some (or even all in some instances)of the traffic on that congested link can be redistributed to otherlinks.

Exemplary embodiments as described herein may conform to any technologyperforming connectivity verification over a set of alternateconnections/paths. Therefore, several different realizations arepossible. Some examples of these realizations are highlighted below.

The method as described in exemplary embodiments may be implemented inMPLS-TP, IETF RFC 5921, with a 1:1 protection scheme using an active anda standby path. The service path may be mapped to either the transportLSP (Label Switched Path) or a PW (Pseudo Wire). Link bandwidthdegradation events may then influence the MPLS-TP protection mechanismsto switch over to an alternate path.

Similarly, PBB-TE (Provider Backbone Bridge Traffic Engineering), IEEE802.1Qay-2009, may implement path protection through a worker path and aprotect path. Mapping for PBB-TE may be similar to that of MPLS-TP.

In network configurations where BFD, IETF RFC 5880, is used to validatelayer 3 IP routes, an impaired link may trigger the blocking of BFDHellos. The traffic or service associated with that route is then forcedto take an alternate path.

In an exemplary embodiment, performance parameters on microwave linksmay be monitored. When degradation of these links reaches a thresholdthat is below a required level, the traffic on these microwave links maybe distributed over other transmission links.

A test signal (e.g. Section 7.7.2/Y.1731) may be used or Synthetic FrameLoss Measurement (SLM) as described in ITU-T recommendation Y.1731 tomonitor the microwave links. If a determination is made that the linksare degraded, the traffic may be throttled down on these links andconsequently the bandwidth of these links is reduced accordingly. Linkdegradation may always imply activation of bandwidth reduction.

The test signal can, for example, be a pseudo-random bit sequence (PRBS)of 2³¹−1 or any other suitable test signal. The test signal can bemapped into the OAM PDU as defined in Y.1731 and the bit errors aremonitored on the links. If the errors exceed a threshold, these linkscan be declared as being degraded and the bandwidth is reduced and theservices that are transported on these links can be distributed on otherlinks that are not degraded or have bandwidth available for transportingthe diverted services.

A service redistribution method in accordance with exemplary embodimentsmay be described with reference to FIGS. 6(A)-6(C). A normal operatingcondition is illustrated in FIG. 6(A). Service paths having a 300 Mbpsbandwidth may be established between nodes 610 and 620. These paths maybe designated as 630 and 640. Services S1 and S2 (having a 50 and 75Mbps requirement respectively) may be assigned to path 630 and serviceS2 and S4 (having 90 and 40 Mbps requirement respectively) may beassigned to path 640. S1 may be a critical service such as voice servicefor example. S2, S3 and S4 may be less critical services such as videoservices or value-added services.

The combined requirement for S1 and S2 is 125 Mbps which can beaccommodated by path 630 in its normal state of 300 Mbps bandwidth.Similarly, the combined requirement for S3 and S4 of 130 Mbps can beaccommodated by path 640 in its normal state of 300 Mbps bandwidth.

Service path 630 may include a plurality of tunnels 631, 633, 635 and637 between a plurality of radio towers 632, 634 and 636 as illustrated.Each of the tunnels may have a 300 Mbps bandwidth. Similarly, servicepath 640 may include tunnels 641, 643, 645 and 647 having a bandwidth of300 Mbps between radio towers 642, 644 and 646.

Service path 630 may experience degradation resulting in reduction to abandwidth of 100 Mbps (in tunnel 635 in this example) and service path640 may experience degradation resulting in reduction to a bandwidth of200 Mbps (in tunnel 645 in this example) as illustrated in FIG. 6(B).

In this state, the combined requirements of S1 and S2 (125 Mbps) cannotbe accommodated by path 630. Due to detection of high frame loss ratio(i.e. degradation) on path 630, services S1 and S2 can be switched topath 640. However, this will also lead to high frame loss ratio on path640.

If switching does not take place, a service disruption is experienced byS1 and S2 on path 630. The combined requirements of S3 and S4 (130 Mbps)can still be accommodated by path 640.

However, path 630 could accommodate one of S1 (50 Mbps), S2 (75 Mbps),S3 (90 Mbps) and S4 (40 Mbps) since each of these require less than theavailable bandwidth of 100 Mbps. Path 630 could also accommodate thecombined requirements of S1 (50 Mbps) and S4 (40 Mbps) since theircombined requirement (90 Mbps) is less than the available bandwidth of100 Mbps.

Path 640 with its current available bandwidth of 200 Mbps canaccommodate each of the following individual and combined services: S1,S2, S3, S4, S1/S2, S1/S3, S1/S4, S2/S3, S2/S4, S3/S4, S1/S2/S4 andS1/S3/S4.

According to exemplary embodiments, the services can be redistributed.In an exemplary redistributable service allocation, as illustrated inFIG. 6, service S2 can be switched to path 640 and service S4 can beswitched to path 630. In this state, services S1 and S4 are carried bypath 630 and services S2 and S3 are carried by path 640.

The combined requirements of S1 and S4 (90 Mbps) can be accommodated bypath 630 even in its degraded state (with 100 Mbps). Similarly, thecombined requirements of S2 and S3 (165 Mbps) can be accommodated bypath 640 in its degraded state (200 Mbps).

Services S1 and S2 can be grouped over one path (630) as illustrated inFIGS. 6(A). Services S3 and S4 can be grouped over another path (640).That is, multiple services can be grouped for transmission over onepath.

By implementing exemplary embodiments, more services can be supported bycontinuously using the degraded link at lower bandwidth. Some importantservices can maintain very high availability even during bandwidth/linkdegradation. This is of particular importance in microwave networkapplications as the bandwidth resource is limited.

Performance monitoring of the microwave links can be carried out, butnot limited, by the following possible methods: (i) A test signal may besent as defined in ITU Recommendation Y.1731 for monitoring errors anddeclaring the link as being degraded at various threshold values; and(ii) Synthetic Frame Loss (SLM) measurement as defined in the latestY.1731 may be used.

In order to ensure proper functioning of the service distribution (or,redistribution) policy, a message is sent to each end of the pathindicating the current maximum bandwidth that can be utilized on thepath as well as communicating with intermediate points along the path.The current maximum bandwidth of the path cannot be exceeded as a resultof redistributing the services. Alternatively, messages may be exchangedor sent between the endpoints of the paths and/or intermediate pointsalong the path to negotiate the redistribution of the services on thepath.

Exemplary embodiments may be implemented in ring andnecklace/multi-homed networks. Implementation in an aggregation ring isdescribed with reference to FIG. 7. Ring 700 includes nodes 710, 720,730 and 740 (with corresponding switches 712, 722, 832 and 742) andlinks L1, L2, L3 and L4 between the nodes. The services traversing thering 700 from nodes 710, 720 and 740 are aggregated into node 730.

Each of the nodes 710, 720 and 740 can have multiple serviceredistribution functions associated therewith. These functions aredesignated as 717, 727 and 747 respectively. For each of the servicesoffered by nodes 710, 720 and 740, redistribution functions may beconfigured over (active) service paths 715, 705/725 and 745 to node 730.The passive paths (not illustrated) can be routed in the oppositedirection of the associated active path.

Node 730 may detect impairments on paths 705 and/or 715. According toexemplary embodiments, parts of the services to nodes 710 and 720 (fromnode 730) traversing paths 715 and 705 may be blocked. The services canthen be redistributed on the (currently) passive paths associated (inopposite direction) with paths 745, 725 and 705 from node 730 to nodes740, 720 and 710 respectively.

Implementation of exemplary embodiments in a necklace/multi-homednetwork is illustrated in FIG. 8. Network 800 includes nodes 810, 820,830 and 840 (with corresponding switches 812, 822, 832 and 842) andlinks L1, L2 and L3 between the nodes. As with the aggregation ring 700of FIG. 7, some of the nodes can have multiple service redistributionfunctions. In network 800, nodes 810 and 820 have multiple serviceredistribution functions associated therewith. These functions aredesignated as 818 and 828 respectively.

In network 800, there are multiple (two in this case) exit points foreach service. Nodes 830 and 840 provide access to another connectivitydomain 850. The service paths 815 and 825 (i.e. active service paths)are monitored to determine if they offer connectivity (i.e. adequatelink capacity). This information (i.e. whether they offer connectivity)is communicated towards domain 850 from nodes 830 and 840. No directcommunication path is needed between 830 and 840 to exchange informationabout the states of the links.

If active service path 815 between nodes 810 and 830 is degraded, thenthe passive service path 816 between nodes 810 and 840 is used to sendservice from node 810 to node 840. Similarly, if active service path 825between nodes 820 and 840 is degraded, then the passive service path 826between 820 and 830 is used to send service from node 820 to node 830.In any of these arrangements, it is not impossible to use one path forboth services if another path is degraded as long as the non-degradedpath provides the required bandwidth.

The load-sharing and redistribution functionality in the necklacenetwork 800 is similar to that of ring network 700. The impairmentsignaling is performed by blocking the service paths. Therefore, theload-sharing method described with reference to network 800 does notintroduce any new information that needs to be synchronized between theredistribution functions on nodes 830 and 840. Protections schemesoffering one active path already have mechanisms for synchronizing theactive/passive path state.

Several advantages may be realized by exemplary embodiments asdescribed. Links can be used continuously even with degraded conditions(i.e. at a reduced bandwidth). Links can be used in microwave networksor other point to point communications. Exemplary embodiments asdescribed for handling variable bandwidth networks can be implementedutilizing existing technologies.

Service re-routing is facilitated over complex topologies with severalingress and egress points triggered by impairment conditions on variablebandwidth links. Information about the impairment condition iscommunicated to a limited set of network elements and network levelsynchronization is not used. The response time for addressing impairmentconditions is short, typically less then 50 ms. Exemplary embodimentscan leverage existing technologies.

The invention has been described with reference to particularembodiments. However, it will be readily apparent to those skilled inthe art that it is possible to embody the invention in specific formsother than those of the embodiment described above. The describedembodiments are merely illustrative and should not be consideredrestrictive in any way. The scope of the invention is given by theappended claims, rather than the preceding description, and allvariations and equivalents which fall within the range of the claims areintended to be embraced therein.

What is claimed is:
 1. A method for adjusting bandwidth in acommunications network including a plurality of nodes connected overmultiple links and having a plurality of services running on the links,the method comprising the steps of: detecting an impairment of a link,the impairment invoking a reduction in bandwidth available to theservices running on the link; communicating information about theimpairment to other nodes in the network; and redistributing servicesbetween the links to limit a bandwidth required by services running onthe impaired link to a value not exceeding the bandwidth available onthe impaired link.
 2. The method of claim 1, wherein the redistributionof services comprises moving at least one service from the impaired linkto another link.
 3. The method of claim 1, wherein the redistribution ofservices comprises: exchanging services between the impaired link and atleast one additional link.
 4. The method of claim 4, wherein theexchanging of services comprises: routing a service from the impairedlink to another link and routing a service from the other link to theimpaired link.
 5. The method of claim 1, further comprising: detecting areduction in the link impairment, the reduction resulting in theimpaired link regaining its original bandwidth; and returning theredistributed services to their original paths.
 6. The method of claim1, further comprising: redistributing real-time services.
 7. The methodof claim 6, further comprising: redistributing best effort services. 8.The method of claim 1, further comprising: specifying a threshold valuefor a link buffer data; redistributing at least one service from a pathassociated with the link if buffer data exceeds the threshold.
 9. Themethod of claim 8, wherein the threshold value is a specified percentageof the link bandwidth.
 10. The method of claim 1, wherein theinformation about the impairment includes bandwidth of the impairedlink.
 11. The method of claim 1, further comprising: communicatingchanges in the network resulting from the re-distribution to a controlplane or network management system.
 12. A node in a communicationsnetwork including a plurality of nodes connected over multiple links andhaving a plurality of services running on the links, the nodecomprising: an impairment detection module for detecting an impairmentin a link used by the node, the impairment invoking a reduction inbandwidth available to the services running on the link; a communicationinterface for communicating information about the impairment to othernodes in the network; and an impairment resolution module forredistributing services between the impaired link and at least one otherlink.
 13. The node of claim 12, wherein the communication interfaceprovides communication between the impairment detection module and theimpairment resolution module.
 14. The node of claim 12, wherein thereduced bandwidth resulting from link impairment is greater than abandwidth required by the redistributed services.
 15. The node of claim12, wherein the communication interface comprises: a first functionalunit for providing communication between the impaired link and othernodes in the network; and a second functional unit for providingcommunication between the impairment detection module and the impairmentresolution module.
 16. The node of claim 12, wherein the communicationinterface communicates information on services running on the impairedlink.
 17. The node of claim 12, wherein the communication interfacereceives available bandwidth information from the other nodes, theavailable bandwidth information corresponding to links being used by theother nodes.
 18. The node of claim 17, wherein the communicationinterface receives service information for services running the links.19. The node of claim 12, wherein the impairment detection module, thecommunication interface and the impairment resolution module areimplemented as one hardware module.
 20. The node of claim 12, where eachof the impairment detection module, the communication interface and theimpairment resolution module are implemented as separate hardwaremodules.